Abstract. The terrestrial ring current is an electric current flowing toroidally around the Earth, centered at the equatorial plane and at altitudes of-10,000-60,000 km. Changes in this current are responsible for global decreases in the Earth's surface magnetic field, which are known as geomagnetic storms. Intense geomagnetic storms have severe effects on technological systems, such as disturbances or even permanent damage to telecommunication and navigation satellites, telecommunication cables, and power grids. The main carriers of the storm ring current are positive ions, with energies from -1 keV to a few hundred keV, which are trapped by the geomagnetic field and undergo an azimuthal drift. The ring current is formed by the injection of ions originating in the solar wind and the terrestrial ionosphere. The injection process involves electric fields, associated with enhanced magnetospheric convection and/or magnetospheric substorms. The quiescent ring current is carried mainly by protons of predominantly solar wind origin, while geospace activity tends to increase the abundance (both absolute and relative) of O + ions, which are of ionospheric origin. During intense magnetic storms, the O + abundance increases dramatically, resulting in a rapid intensification of the ring current and an O + dominance around storm maximum. This compositional change affects, among other processes, the decay of the ring current through the species-and energy-dependent charge exchange and wave-particle scattering loss. Energetic neutral atoms, products of charge exchange, enable global imaging of the ring current and are the most promising diagnostic tool of ring current evolution. This review will cover the origin of ring current particles, their transport and acceleration, the effects of compositional variations in the ring current, the effects of substorms on ring current growth, and the dynamics of ring current decay with an emphasis on the process of charge exchange and the potential for wave scattering loss.

Abstract. This paper attempts to summarize the current understanding of the storm/substorm relationship by clearing up a considerable amount of controversy and by addressing the question of how solar wind energy is deposited into and is dissipated in the constituent elements that are critical to magnetospheric and ionospheric processes during magnetic storms. (1) Four mechanisms are identified and discussed as the primary causes of enhanced electric fields in the interplanetary medium responsible for geomagnetic storms. It is pointed out that in reality, these four mechanisms, which are not mutually exclusive, but interdependent, interact differently from event to event. Interplanetary coronal mass ejections (ICMEs) and corotating interaction regions (CIRs) are found to be the primary phenomena responsible for the main phase of geomagnetic storms. The other two mechanisms, i.e., HILDCAA (high-intensity, long-duration, continuous auroral electrojet activity) and the so-called RussellMcPherron effect, work to make the ICME and CIR phenomena more geoeffective. The solar cycle dependence of the various sources in creating magnetic storms has yet to be quantitatively understood.

Abstract. Using the Dst index, more than 1200 geomagnetic storms, from weak to intense, spanning over three solar cycles have been examined statistically. Interplanetary magnetic field (IMF) and solar wind data have also been used in the study. It is found that for more than 50% of intense magnetic storms, the main phase undergoes a two-step growth in the ring current. That is, before the ring current has decayed significantly to the prestorm level, anew major particle injection occurs, leadingto a further development of the ring current, and making Dst decrease a second time. Thus intense magnetic storms may often be the result of two closely spaced moderate storms. The corresponding signature in the interplanetary medium is the arrival of double-structured southward IMF at the magnetosphere.

Abstract:27 Since the discovery of the Van Allen radiation belts over 50 years ago, an explanation for Text:41

No abstract

Abstract. We show that distinct changes in scaling parameters of the D st index time series occur as an intense magnetic storm approaches, revealing a gradual reduction in complexity. The remarkable acceleration of energy release -manifested in the increase in susceptibility -couples to the transition from anti-persistent (negative feedback) to persistent (positive feedback) behavior and indicates that the occurence of an intense magnetic storm is imminent. The main driver of the D st index, the V B South electric field component, does not reveal a similar transition to persistency prior to the storm. This indicates that while the magnetosphere is mostly driven by the solar wind the critical feature of persistency in the magnetosphere is the result of a combination of solar wind and internal magnetospheric activity rather than solar wind variations alone. Our results suggest that the development of an intense magnetic storm can be studied in terms of "intermittent criticality" that is of a more general character than the classical self-organized criticality phenomena, implying the predictability of the magnetosphere.

[1] The complex system of the Earth's magnetosphere corresponds to an open spatially extended nonequilibrium (input-output) dynamical system. The nonextensive Tsallis entropy has been recently introduced as an appropriate information measure to investigate dynamical complexity in the magnetosphere. The method has been employed for analyzing D st time series and gave promising results, detecting the complexity dissimilarity among different physiological and pathological magnetospheric states (i.e., prestorm activity and intense magnetic storms, respectively). This paper explores the applicability and effectiveness of a variety of computable entropy measures (e.g., block entropy, Kolmogorov entropy, T complexity, and approximate entropy) to the investigation of dynamical complexity in the magnetosphere. We show that as the magnetic storm approaches there is clear evidence of significant lower complexity in the magnetosphere. The observed higher degree of organization of the system agrees with that inferred previously, from an independent linear fractal spectral analysis based on wavelet transforms. This convergence between nonlinear and linear analyses provides a more reliable detection of the transition from the quiet time to the storm time magnetosphere, thus showing evidence that the occurrence of an intense magnetic storm is imminent. More precisely, we claim that our results suggest an important principle: significant complexity decrease and accession of persistency in D st time series can be confirmed as the magnetic storm approaches, which can be used as diagnostic tools for the magnetospheric injury (global instability). Overall, approximate entropy and Tsallis entropy yield superior results for detecting dynamical complexity changes in the magnetosphere in comparison to the other entropy measures presented herein. Ultimately, the analysis tools developed in the course of this study for the treatment of D st index can provide convenience for space weather applications.Citation: Balasis, G., I. A. Daglis, C. Papadimitriou, M. Kalimeri, A. Anastasiadis, and K. Eftaxias (2009), Investigating dynamical complexity in the magnetosphere using various entropy measures,

Abstract. The present study attempts to visualize the global equatorial current systems and the proton pressure in the near-Earth magnetosphere based on AMPTE/CCE-CHEM measured proton distributions, which were sorted by the AE index ( "quiet": AE < 100 nT, "active": 100 nT < AE < 600 nT). The data were averaged over 2 years (from January 1985 to June 1987) in order to obtain the necessary spatial resolution with statistical significance. The results provide an average image of proton plasma pressure, proton plasma anisotropy, and current systems as a function of geomagnetic activity. In particular, the changes of pressure anisotropy with local time and the noon-midnight pressure asymmetry are studied and correlated to the current systems out of the equatorial plane that generate the closure circuits. Moreover, we identify and spatially locate two different current systems for the quiet period (the ring current and the inner portion of the quiet thne cross-tail current) and three different current structures for the active period (the ring current, the partial ring current, and the region 2 current).